Preliminary studies indicate that exercise training or a single bout of exercise causes in vitro and in vivo amino acid incorporation into protein to be decreased in muscle. Since training does not depress the quantity of muscle protein in relation to body weight, it seems likely that protein degradation may also be decreased. The primary purpose of the proposed research is to study control of muscle protein synthesis and protein degradation in response to exercise training. Three different levels of muscle organization will be studied to try and determine both the effects of exercise and, where possible, the mechanism that causes these effects. The three levels of organization will be: (1) in vivo (red and white muscle from intact animals) (2) perfused muscle, and (3) in vitro (tissue slice, isolated muscle fibers, homogenate, etc.). Labeled amino acid will be injected into the intact animal and protein synthesis will be determined by measuring the rate of disappearance of label from protein (correcting for reutilization). In the perfused muscle studies, similar kinds of techniques will be utilized but the mechanism and mediating factors (hormones, muscle contraction, etc.) underlying the changes found in the intact animal will be studied. The in vitro studies will delve further into the mechanisms with the study of individual processes and enzymatic reactions. This study will also include experiments concerning the effect of exercise on in vivo protein synthesis and degradation in heart and liver, but not to the extent investigated in skeletal muscle.